1. Field of the Invention
The present invention relates to a keyboard device, and in particular to an illuminant keyboard device.
2. Description of Prior Art
In order to provide convenience for operator in a dark environment or a dim room where enough illumination light is not provides, an illuminant device is provided for keyboards of computers or mobile phones and then operator can clearly recognize the letters of the keycaps.
Reference is made to FIG. 1 and FIG. 2, which are respectively a sectional view and a partially enlarged view of a conventional illuminant keyboard device. The keyboard device 10 includes a bottom frame 100, a plurality of keying units 110, a membrane switch 120, a plurality of elastic member 130 and an illuminant module 140.
The bottom frame 100 has a plurality of latch parts 102. The keying units 11 are disposed on the bottom frame 100. Each keying unit 110 includes a keycap 112 which can move upward and downward corresponding to the bottom frame 100 and a linking mechanism 114 interposed between the bottom frame 100 and the keycap 112 so as to be able to expand and contract and thereby support the keycap 112. In this embodiment, the linking mechanism 104 intersects in the shape of X to form a scissor structure.
The membrane switch 120 is interposed between the bottom frame 100 and the keying units 110. The membrane switch 120 may be made of materials having optical transparency and is provided with conductive traces (not shown) and contacts 122 thereon. The contacts 122 are electrically connected to the conductive traces and correspond to the keycaps 112.
The elastic members 130 are interposed between the membrane switch 120 and the keycaps 112 and located above the contacts 122. The elastic members 130 are always elastically pushed up the keycaps 112 toward the standby position by urging force.
If a desire keycap 112 is pressed against the elastic force of the elastic member 130, the elastic member 130 is gradually deformed and touches the membrane switch 120. As the result, the contacts 120 formed on the membrane switch 120 are conducted, and thus the membrane switch 120 is turned on and generates a signal corresponding to the letters.
The illuminant module 140 includes a plurality light emitting diodes (LEDs) 142, a light guide plate 133 and a diffusing plate 146. The light guide plate 144 has a light-incident surface 1440, a light-emitting surface 1442 and a plurality of via-holes 1444 allowing the latch parts 102 protruded therethrough. The LEDs 142 is disposed on the light-incident surface 1440 and emitting light to the light-incident surface 1440. Light emitted by the LED 142 is incident on the inside of the light guide plate 144 from the light-incident surface 1440 and emitting by light-emitting surface 1442.
The diffusing plate 146 is interposed between the light guide plate 144 and the membrane switch 120. Light emitted from the light-emitting surface 1442 is then incident to the diffusing plate 146. The diffusing plate 146 diffuses light and then generates a surface light source with uniform illumination. The diffusing plate 146 includes a plurality of through-holes 1460 allowing the latch parts 102 protruded therethrough and the diameter of each of the through-holes 1460 is equal to the diameter of each of the via-holes 1444 formed on the light guide plate 144.
Part of light emitted by LEDs 142 is incident to light guide plate 144 from the light-incident surface 1440 and passing through the inside of the light guide plate 144 and emitting by the light-emitting surface 1442, and part is refracted by the hole-wall of the via-holes 1444. Because the diameter of each of the via-holes 1444 is equal to the diameter of each of the through-holes 1460, the light refracted from the via-holes 1444 are directly traveling to the keying units 110 through the through-holes 1460. Therefore, a part of light leaks out from gaps located between each two keying units 110, and the luminance of the illuminant keyboard device 10 is non-uniform and increases the difficulty of recognizing the letters of the keycaps 112.